mpeters951

Yes, I've searched.

Haynes manual blows on this procedure.

Other thread(s) seem to indicate using the Schrader valve at the back of the compressor; is this positively correct ?

What is the valve next to the shock tower for ? Is this high or low pressure ?

Anyone have direct experience with Fox Tool Supply (advert in Excellence) and their HC12a potion ?

Help greatly appreciated.

josephsc

I've seen the low-pressure line in two different locations. For a late-944, underneath the car, near the AC compressor -- PITA to get to. This is probably what the Haynes manual shows. For an 88 951S and 86 951, I've seen them located at the top of the engine compartment near the cam-tower, driver-side -- much easier to get to.

Mike S

The easiest way to tell is that the high pressure line is small in diameter, while the low pressure line is larger. Do NOT....I repeat...Do NOT try to put R-12 through the high pressure side. This is a good way to blow up the can and end up picking metal out of your hands for weeks.

I have an 87 and mine is located right next to the A/C compressor facing down towards the ground. You may also want to get a bucket of hot water to put the can in as it can freeze up when you start sending it through the lines.

Porsche-O-Phile

How about on the early n/a cars? I believe for those you must use the fill port on the rear of the compressor, right?

mpeters951

As the system is low enough to have tripped the low pressure sensor and cut off the compressor, can the first can of R12 be introduced with out "jumpering" such that the sensor allows the compressor to to come on and continue the process?

Or is the situation such that the compressor must be live to pull in any of the R12?

sm

MPeters:

Did you pull a vacuum on your A/C system? If so, the system will easily suck one can of R-12 into the system withOUT the compressor running.

The proper way is to pull a vacuum and hook up a set of gauges to your car.

Here's the info you need: Charging Information

Porsche-O-Phile

IIRC the compressor must be running to add any refrigerant. The first can might be able to be introduced without (expecially if there's a vaccum in the system to begin with), but I haven't seen it done this way.

Is your system totally out of refrigerant or is it just low?

Reason I ask is a system that very slowly and gradually loses refrigerant can end up getting "topped off" every once in a while but this tends to change the concentration of refrigerant to compressor oil. Think of it this way: if (over a long time) someone keeps shoveling can after can after can of refrigerant without adding the corresponding amount of oil, the system will gradually have all refrigerant and no oil - resulting in a compressor failure.

The absolute best thing to do is completely evacuate the system of ALL oil and refrigerant and then add known quantities of each - that way you're starting from ground zero and KNOW what's in there and that it's right. Unfortunately, this is also the most expensive option.

If you do have a completely empty / evacuated system, I'd recommend adding the oil first - for the good of your compressor.

Jeremy Himsel

There is no reason to jumper the AC to add refrigirant. On a completely empty system, the pressure/amount in a can is enough to get the compressor to start cycling. Jumping the switch is actually a bad thing (however minor) as it takes freon flow to carry the oil throughout the system. Jumping the system for too long can allow the compressor oil to run dry and do damage.

gstreev

On my 89 I'm pretty sure the high pressure is up by the shock tower, lo pressure (fill) side
down by the compressor. With the car running check the pressure at both points to be sure.

Tomas L

How much oil is needed for an empty system and where should one add the oil?

Porsche-O-Phile

I think it's two cans' worth, but I'll check. It can be added at the same low pressure port as the refrigerant - unless you're lucky enough to be able to find r12 with oil mixed in already. That's pretty rare though.

Charlotte944

I've seen three different configurations for service valves.

With the early cars the low side service fitting is at the front of the compressor, so you need to loosen the drive belt, connect the service hose, tension the belt, and so forth. The high side fitting is forward of the reciever/dryer.

For the late cars, I have seen two configurtations. In both cases there is a low side fitting at the rear of the compressor, and the high side fitting is on the driver side shock tower. In the third configuration, there is a low side fitting at the rear of the compressor, plus a low and high side fitting on the driver side shock tower. This is how my '86 951 and '87 NA are configured.

Charlotte944

This all depends on just how low the system pressure is. Chances are you should be able to get the compressor to run by opening the fill valve, but if it doesn't you have to jumper the low pressure switch.

Porsche-O-Phile

For the '86-'88 951's with 33.5 ounce r12 capacity the oil is 100 cm^3 or 3.3 ounces. For the '89-'91 versions the spec is 80 cm^3 or 2.8 ounces of oil. Why the change I dunno.

In any event my earlier estimate is a bit high (I was thinking of the early cars which require 9.3 ounces of oil); IIRC the oil cans are like 4 ounce shots or something - I'd have to look again (don't have one handy). You could also measure out the proper quantity and pour it into the compressor prior to installing it - that way you'd have the exact right amount.

ehall

here's a "I don't know crap about a/c question". Is R12 the original type of freon used in the original compressor? If so, what is used in the newer "conversions?" Quess why I want to know?